Stabilized nylon 6,6 yarn has been used for some time as a preferred yarn for automotive airbag cushion applications. Relatively high strength nylon yarns having a tenacity above 8.0 grams/denier are commonly used in automotive airbag applications.
Nylon 6,6 yarn when stabilized generally performs well in aging tests. Airbags must pass aging tests to be employed by automotive manufacturers. Manufacturers provide relatively strict requirements for the strength performance of airbags after such airbags have endured significant amounts of aging at high temperatures and high humidity. Automobiles are exposed to high temperatures and high humidity for many years, and thus airbags within deployment modules installed in automobiles also must retain their strength so that when and if airbag deployment occurs, the airbag will be capable of operating properly.
In the past, it has been relatively rare that manufacturers have employed polyester yarn for automotive airbag applications. One reason is that polyester tends to deteriorate over time at high temperature and high humidity. Thus, polyester has not been a favorite candidate yarn for airbags in part because of inadequate performance in humidity aging tests.
It is known that the tenacity of polyester can be increased in some instances by further drawing the polyester. Tenacity is also known as tensile strength. Tenacity is one measure of the strength of polyester yarn. One drawback to further drawing polyester yarn to achieve high levels of tenacity relates to the excessive costs associated with drawing processes in such manufacture.
In the recent past there has been no cost advantage in the use of polyester yarn having a tenacity of about 8–9 as compared to conventional stabilized nylon 6,6 yarn which is in widespread use for airbag applications. Conventional polyester yarns available for airbag applications still sometimes fail to pass the relatively strict automotive industry requirements for long term strength after such “hydrolytic” aging.
Current industrial applications for polyester usually do not require that the polyester yarn withstand relatively high temperatures and high humidity while still maintaining a relatively high tensile strength for a long period of time. Thus, there is no ready information at hand in the prior art that identifies what polyester yarn types could be suitable for airbag use.
Polyester chemistry is a highly unpredictable art. The task of finding or formulating a polyester yarn that will perform in airbag applications in an extremely difficult task, and often requires a significant expenditure of research effort and time.
Airbag applications, in contrast to other typical polyester end use applications, typically require that a yarn maintain at least at about 85% of its strength after several thousand hours of exposure to relatively high humidity and high temperature environments. Most polyesters that are known in the industry cannot meet such requirements. It would therefore be desirable to discover, identify, characterize, and establish both physical and chemical characteristics of what products and processes will provide a polyester yarn that will pass stringent testing requirements for airbag applications.
In general, the airbag manufacturing industry needs reliable and effective alternatives to the use of nylon 6,6 for airbag applications. A lower cost alternative to nylon 6,6 would be desirable. Furthermore, the discovery of a manner or a method for manufacturing, measuring, evaluating or applying polyester yarn in a manner that will pass strict automotive testing requirements would be helpful. The identification and measurement of both physical and chemical properties in the polyester yarn that undesirably lead to deterioration of the yarn would be helpful. Once these properties have been identified and correlated to airbag testing requirements, it may be possible to identify materials for airbag applications.
A currently pending, commonly owned and published U.S. patent application Ser. No. 10/041,376 and titled “Airbag Made from Low Tenacity Yarns” (Milliken file number 5287) published on Jan. 8, 2002. This publication reveals that in certain specific applications airbag systems may be designed in which a yarn having a tenacity of less than about 8.0 grams per denier can be employed in some applications. This disclosure specifically advises placing the seams of the airbag in shear to achieve this effect. Structural modifications are made to the airbag to achieve a satisfactory configuration.